The present invention relates to a solid-state laser device which can be used in the industrial field, medical field, and the like.
A conventional solid-state laser device generally comprises an arrangement wherein an optical fiber is connected to a laser generator to guide a laser beam to an arbitrary position, or an arrangement wherein a laser resonator including a solid-state laser medium is housed in a housing different from that for a pumping light source, and the laser resonator and the light source are connected via an optical fiber so that they can be disassembled from each other, as disclosed in U.S. Pat. No. 4,665,529.
FIG. 1 shows the arrangement of a conventional solid-state laser device. Reference numeral 20 denotes a semiconductor laser for generating a laser beam having a wavelength of 809 nm; 21, a laser beam emitted from the semiconductor laser 20; 22, a collimator lens; 23, a focusing lens; and 24, a solid-state laser medium (e.g., Nd:YAG). A coating film which has a transmittance of 99.5% for a wavelength of 809 nm and a reflectance of 99.9% for a wavelength of 1.064 .mu.m is formed on a facet 24a of the solid-state laser medium 24, and a coating film which has a transmittance of 99.9% for a wavelength of 1.064 .mu.m is formed on the other facet 24b. Reference numeral 25 denotes a reflection mirror. A coating film which has a reflectance of 97% for a wavelength of 1.064 .mu.m is formed on a facet 25a of the reflection mirror 25. Reference numeral 27 denotes a focusing lens; 28, an optical fiber cable; 29, an output laser beam; and 30, a device main body.
The operation of the conventional solid-state laser device with the above-mentioned arrangement will be explained below. The laser beam 21 having a wavelength of 809 nm, which is generated by the semiconductor laser 20, is shaped into a collimated beam by the collimator lens 22, and the collimated beam is focused on the facet 24b of the solid-state laser medium 24 by the focusing lens 23, thus pumping the solid-state laser medium 24. Light pumped in the solid-state laser medium 24 reciprocates between the facet 24a and the facet 25a of the reflection mirror 25 to cause laser generation, and then emerges from the reflection mirror 25 as a laser beam 26 having a wavelength of 1.064 .mu.m. Thereafter, the laser beam 26 is focused by the focusing lens 27, and is incident on an incident end 28a of the optical fiber cable. The laser beam 26 is guided to a distal end portion 28b via the optical fiber cable 28, and emerges from the optical fiber cable as the output laser beam 29. For this reason, the output laser beam can be irradiated at an arbitrary position separated from the device main body 30.
FIG. 2 shows the arrangement of a second conventional solid-state laser device. Reference numeral 20 denotes a semiconductor laser for generating a laser beam having a wavelength of 809 nm; 21, a laser beam emitted from the semiconductor laser 20; 22, a collimator lens; 23, a focusing lens; and 24, a solid-state laser medium (e.g., Nd:YAG). A coating film which has a transmittance of 99.5% for a wavelength of 809 nm and a reflectance of 99.9% for a wavelength of 1.064 .mu.m is formed on a facet 24a of the solid-state laser medium 24, and a coating film which has a transmittance of 99.9% for a wavelength of 1.064 .mu.m is formed on the other facet 24b. Reference numeral 25 denotes a reflection mirror. A coating film which has a reflectance of 97% for a wavelength of 1.064 .mu.m is formed on a facet 25a of the reflection mirror 25. Reference numeral 40 denotes an optical fiber cable; 41, a focusing lens; 42, an output laser beam having a wavelength of 1.064 .mu.m; 43, a device main body which houses the semiconductor laser 20 and its driving circuit; and 44, a housing which houses a solid-state laser generation unit. Reference numerals 45 and 46 denote optical fiber connectors. The device main body 43, the optical fiber cable 40, and the generation unit housing 44 can be disassembled from each other.
The operation of the second conventional solid-state laser device with the above-mentioned arrangement will be described below. The laser beam 21 having a wavelength of 809 nm, which is generated by the semiconductor laser 20, is shaped into a collimated beam by the collimator lens 22, and the collimated beam is focused by the focusing lens 23. The focused beam is incident on an incident end 40a of the optical fiber cable, and propagates through the optical fiber cable 40. Thereafter, the laser beam 21 emerging from an exit end 40b of the optical fiber cable is focused again by the focusing lens 41 onto the facet 24a of the solid-state laser medium 24, thus pumping the solid-state laser medium 24. Light pumped in the solid-state laser medium 24 reciprocates between the facet 24a and the facet 25a of the reflection mirror 25 to cause laser generation, and then emerges from the generation unit housing 44 via the reflection mirror 25 as the output laser beam 42 having a wavelength of 1.064 .mu.m.
However, according to the examination of the present inventors, in the solid-state laser device having the arrangement of the first prior art, since the light transmission characteristics of the optical fiber have wavelength dependence, when, for example, a quartz optical fiber is used, it is difficult to guide light components in a wavelength range exceeding 2.5 .mu.m and a wavelength range below 300 nm through this fiber, thus preventing a practical application.
In particular, when such a solid-state laser device is used in the medical field, water contents contained in an affected part must be heated to heat the affected part. In order to achieve this object, it is effective to irradiate a laser beam having a wavelength of about 2.8 .mu.m, as a wavelength which is most easily absorbed by water, onto the affected part. More specifically, the above-mentioned device cannot effectively guide a laser beam having a wavelength of 2.8 .mu.m, which is most required in the medical field.
On the other hand, the solid-state laser device having the arrangement in the second prior art aims at replacing the solid-state laser medium or preventing heat generated upon driving of the semiconductor laser in the device main body from influencing the solid-state laser generation unit. For this purpose, the laser generation unit is housed in a housing different from the device main body, and the distal end portion of the fiber has a large size, thus considerably retarding the guiding performance of the generated laser beam to an arbitrary position.